public void TestRotate()
{
var turtle = new Turtle(new Vector(0, 0), 0.0, ImmutableStack<Turtle.TurtleState>.Empty, dummy, Colors.Black);
var rotated = turtle.Rotate(Math.PI / 2);
var expected = Math.PI / 2;
var actual = rotated.Angle;
Assert.AreEqual(expected, actual);
}